Sahih Muslim Book 6, Hadith Number 2569.

Chapter : Excellence of fasting.

Sahl b. Sa’d (Allah be pleased with him) reported Allah’s Messenger (may peace be upon him) as saying: In Paradise there is a gate which is called Rayyan through which only the observers of fast would enter on the Day on Resurrection. None else would enter along with them. It would be proclaimed: Where are the observers of fast that they should be admitted into it?-and when the last of them would enter, it would be closed and no one would enter it.